avatarworf

I must have spoken too soon.

After saying just the other day that we'd travelled 30,000km on our custom made bikes without a problem, yesterday we discovered a crack in Andrew's frame. Just a small one, where the back rack attaches to the frame. We found a motorbike shop run by a French guy here in Phnom Penh and he seemed pretty competent so we're getting it fixed up now.

My question is, assuming he does a reasonable job of welding the crack, is the frame going to be as strong as before, stronger or is this just a sign of imminent demise that we'll only put off by fixing?

Also, what is the most likely cause of the crack? The French guy said it was overloading. Plausible. We haven't given the bike any knocks that we know about.

What kind of life would you expect out of a well built touring bike - 50,000km? Nothing lasts forever I guess, though I wish it would...

Rowan

You are talking about the drop-out? If you get that repaired, I would think about getting a competent framebuilder to replace the entire drop out sometime sooner rather than later... and that could be in years' time.

There could be several causes, but overloading might be the most feasible, especially if you have been riding rough roads and there has been any sway in the rack. There's a case for the rack being the weakest link -- having it give way before the dropout.

My frame is an off the shelf job and is closing in on 60,000km. I broke the right rear dropout when the bike was blown over in a gust and landed on the skewer -- the force was at just the right angle to break the dropout. The bike was not loaded at the time (and if it was, the break probably wouldn't have occurred).

I repaired it by braze welding and it has held up so far for over 700km, but the dropout *will* be replaced some time into the future. I did ride a 400km after the breakage because I didn't realise it had happened, but then wondered why there was a knocking noise and my shifting with new components was off.

What does the builder of the frame say?

avatarworf

I had to look up what a drop out was! We ride a lot but my technical names knowledge is not so good....

If I understand correctly, the dropout is where the frame attaches to the wheel, next to the cassette. The crack is not there. It is where the top of the rack attaches to the frame, quite near the seat post. I will post pictures later but Andrew has run off to pick up the bicycle and taken the camera with him.

Haven't talked to the framebuilder yet.

Maxwell

Well, the seatstays, where your crack is, are not very highly stressed in riding. was it just the rack attachment itself, the braze on, coming off the tube? The seatstays can usually tolerate all sorts of damage, so your repair should be fine.

avatarworf

Here's a picture. Andrew is now back and apparently the bike is looking pretty good. A few hundred kilometers on the roads of Cambodia and Laos ought to test things...

avatarworf

Here's the after picture. A pretty good job I think!

bhchdh 

Looks like a great repair job.

lighthorse

Now that sucks for sure. I'll bet the frame builder will say that you had too big of a load on the rear rack which caused the failure. The failure seems to be right in the original weld/braze. Maybe someone can fix it for the rest of your trip.

northboundtrain

That crack is definitely the result of metal fatigue due to the rack swaying back and forth. You should very carfully inspect the rack attachment point on the other seat stay, because once one side cracks, the sway becomes much more exaggerated, and the other side is stressed to a greater extent. Since you've evidently found a competent welder/brazer, you might have him rienforce the other side just to be safe. I cracked a frame in a similar location -- where the seat stay mounts to the seat cluster. I'm sure it was due to rack sway as well. Lashed it together with parachute chord and road another 250 miles home. By then the other side was cracking and about to fail. I welded and brazed it back together and added a big brass fillet on both seat stays. It's holding up well so far.

Bacciagalupe

Well, seems to me that 30,000km isn't too shabby, and there are worse places to get a crack. I agree that you should keep an eye on the rack mounts, just glance at it every once in awhile.

I highly recommend you pick up a few rubber-coated P-clamps. If the rack mount breaks again, you can use the P-clamps indefinitely.

It could be the weld, but (as a non-framebuilder ) it also seems to me like that is an inherently weak design. Most of the rack-mounts I've seen are drilled into the seat stays, rather than welded on like that.

If you have the time or inclination, you might want to put a post (with the pics) into the Framebuilder's subforum, see if they have any thoughts or recommendations.

avatarworf

This is very interesting. What would cause the rack sway? Does that mean the rack wasn't attached equally tightly on all sides and maybe we need to make sure all the screws are screwed in an equal amount? Or....?

markf

Every piece of metal bends or gives to some extent, put a big load on a rack and ride on bumpy roads and the rack will sway back and forth as you ride. The further away the load is from where the rack attaches to the frame, the more leverage the load will exert on the rack mounting points. The heavier the load, the more it will bend and fatigue the mounting points. If the bolts holding the rack onto the frame are loose, the rack will sway more. If you overtighten the bolts, you'll strip them.

Lighten the load on your rear rack (move stuff to the front rack, don't carry so much stuff), move the load forward on the rack to reduce the leverage, and keep checking the bolts to make sure they are snug (but don't strip them). P-clips (also known as cable hanger clamps) to hold the rack on won't look as pretty, and may or may not last as long as your brazed on rack mounts, but it's easier to replace a pair of P-clips than it is to find a good welder /brazer to replace the brazed on mounts and repaint the frame.

If this is the worst that's happened to your frame, you've got nothing to worry about.